In polyurethane foam manufacturing, surfactants are needed to stabilize the foam until the product-forming chemical reactions are sufficiently complete so that the foam supports itself and does not suffer objectionable collapse. High potency silicone surfactants, generally understood to be those which give a high height of rise and little top collapse at minimal use levels, are desirable because foams which collapse to a substantial degree before setting have high densities and objectionable density gradients. In general, it is preferred that the surfactant also gives high airflow performance. The latter feature refers to the ability of air to pass through the foam.
Silicone surfactants for polyurethane foam manufacture typically are materials having siloxane backbones and polyether pendant groups (hereinafter xe2x80x9cCopolymersxe2x80x9d), see for example, U.S. Pat. No. 4,147,847. The importance of the capping group on the ungrafted end of the polyether pendant is well known for many applications such as for flexible foam, see for example, U.S. Pat. No. 4,687,786. It has been taught that a large portion of the polyethers must be capped.
There are a variety of capping groups known such as acyloxy (e.g., acetoxy), alkyl (e.g., methyl), carbonate, or urethane groups. The first two are the most common and each has its own advantages and disadvantages. Acetoxy-capping is a simple convenient process although over 50% of the mass of acetic anhydride used is discarded as waste acetic acid. Essentially 100% capping can readily be achieved but the acetate cap is not hydrolytically stable to acidic or alkaline water. This is a serious deficiency with customers who operate by blending the surfactant into the water/amine premix prior to making foam.
Methyl-capping gives a capped hydroxyl group which is essentially infinitely stable to water/amine premix. Unfortunately, the Williamson Ether process has a number of problems. The capping efficiency is usually below 95% and typically is around 90-93%. This low capping efficiency generally results is not being able to produce as good airflow performance characteristics as observed with acetoxy-capped polyethers. In addition, the process involves handling toxic methylchloride gas as well as separating and disposing of large quantities of NaCl waste. With allyl-terminated polyethers, the harsh conditions used to generate the alkoxide can also rearrange the allyl group to a propenyl group, thus rendering a substantial portion of the polyether unreactive to the subsequent copolymer synthesis step.
Certain types of capping have also been used solely in an intermediary fashion to protect the polyether OH group during hydrosilation to prevent cross-linking (via dehydrocondensation and/or acetal coupling). See U.S. Pat. No. 3,794,673 which employs enol-ether capping. However, after the hydrosilation reaction is completed, the enol-ether group is hydrolyzed off in acidic conditions to generate the desired uncapped polyether copolymer free of cross-links. This same process was used later by E. Wu et al., xe2x80x9cComb polysiloxanes with xcfx89-hydroxyoligo(oxyethylene) side chainsxe2x80x9d, Polymer Bulletin, 20 (1988), 455-461, to produce uncapped Copolymers for use as electrolyte solvents. In none of the above cases was the enol-ether capped Copolymers used to make foam but rather were only intermediates en route to other structures.
The present invention provides the use of Copolymers that offer good potency which have the generalized average formula Mxe2x80x3DxDxe2x80x3yTzMxe2x80x3 wherein
Mxe2x80x3represents (CH3)3SiO,1/2 or R(CH3)2SiO1/2;
D represents (CH3)2SiO2/2;
Dxe2x80x3represents (CH3)(R)SiO2/2;
T represent CH3SiO3/2;
x is from about 20 to about 220;
y is from about 5 to about 34;
z is less than 4;
R is selected from the group consisting of alkyl, aryl and aralkyl groups of 1 to 18 carbons and polyether-containing substituents obtained from polyethers selected from the following two groups (1) and (2):
(1) Bxe2x80x94O(C2H4O)axe2x80x2(C3H6O)bxe2x80x2Rxe2x80x3 polyethers having average molecular masses above 3000 daltons wherein
B is an alkyl bridging group of C2 to C4;
axe2x80x2 and bxe2x80x2 are independently 0 or positive numbers, provided that the total molecular weight of the polyether is above 3000 daltons;
Rxe2x80x3 represents xe2x80x94H, an alkyl group of 1-18 carbon atoms, xe2x80x94C(O)Rxe2x80x2xe2x80x3, xe2x80x94C(O)ORxe2x80x2xe2x80x3 or xe2x80x94C(O)NHRxe2x80x2xe2x80x3 or X;
X represents enol-ether capping moieties derived from Rxe2x80x2xe2x80x32Cxe2x95x90CRxe2x80x2xe2x80x3xe2x80x94Oxe2x80x94Rxe2x80x2xe2x80x3 or cyclic xe2x80x94(CRxe2x80x2xe2x80x32) rxe2x80x94Zsxe2x80x94(CR2)rxe2x80x2xe2x80x94CRxe2x80x2xe2x80x3+CRxe2x80x3xe2x80x94Oxe2x80x94;
r is 1 to 5, s and rxe2x80x2 are 0 through 1, and Z is O, S, or SiRxe2x80x2xe2x80x32;
Rxe2x80x2xe2x80x3 represents xe2x80x94H or a mono-functional alkyl, aralkyl or aryl group of up to 8 carbons; and
(2) Bxe2x80x94O(C2H4O)axe2x80x3(C3H6O)bxe2x80x3Rxe2x80x3 polyethers having average molecular masses in the range 300-3000 daltons wherein
axe2x80x3 and bxe2x80x3 independently 0 or positive numbers, provided that the total molecular weight of the polyether is between 300 and 3000 daltons;
and the B, Rxe2x80x3 and Rxe2x80x2xe2x80x3 moieties are as defined above;
with the provisos that (i) an average of at least one R group per silicone backbone must be a polyether from group (1) or group (2); (ii)there may be more than one polyether from either group; (iii) up to 20% of the propylene oxide (C3H6O) moieties may be replaced with higher alkylene oxide moieties; and (iv) at least one pendant polyether must be capped with an X moiety.
Another aspect of the present invention is polyurethane foam made by the process of the present invention.